The advent of portable electronics and the need for longer battery life calls for new types of voltage regulators, which are very efficient in both low current and high current load conditions. For example, handheld devices such as PDA and cell phones can benefit from high efficiency in both standby and active modes to extend battery life. A very low amount of operating current is of particular importance in standby mode because the devices run in this mode most of the time.
A pulse width modulated (PWM) switching regulator is an efficient regulation scheme during heavy loads. PWM switching regulators offer high efficiency, low output voltage ripple, and good line and load regulation. However, at light loads the PWM regulator has poor efficiency because switching frequency related losses, such as FET switching loss, core loss, gate-drive loss, etc., are not concomitant with decreased output current due to unchanged switching frequency.
Efforts have been made to improve light load efficiency of switching regulators. One method is to operate the switching regulator intermittently based on load demand with fixed peak inductor current. Unfortunately, despite improved light load efficiency, this scheme inherently has a large output ripple voltage.